Magnetic separators have been used for many years for separating desired materials from compounds containing them, by passing the compound through a magnetic field generated by permanent magnets or electromagnets. These magnetic separators are generally of two kinds, utilizing, respectively, so-called “dry” and “wet” separating techniques.
Magnetic separation techniques are disclosed, for example, in SU Author Certificates Nos. 782870 and 1577839, and RU Patent No. 2067887, all by the inventor of the present application. The disclosures in these documents relate to, respectively, “wet” separation utilizing a magneto-gravimetric technique, and “dry” separation utilizing high magnetic induction and high gradient magnetic fields.
For example, RU Patent No. 2067887 discloses a three-stage separation technique. The first and second stages are “dry” processes utilizing, respectively, a magnetic field of relatively low induction value and gradient and a magnetic field of relatively high induction value and gradient. The third stage presents a “wet” process utilizing a magneto-gravimetric technique. However, RU Patent No. 2067887 has no indication as to any optimal implementation of any of these stages.
It is known to use separators of a so-called “drum-type” for separating strongly magnetic fractions by a relatively weak magnetic field. For this purpose, a magnetic field system includes stationary magnets and a drum that is rotated with respect to the magnets. Compounds containing products to be separated are fed into a magnetic field region and magnetic fractions contained in the compounds are adhered to the surface of the rotating drum in the vicinity of the magnets, while non-magnetic fractions continue their flow away from the magnetic field region. The adhered products are removed from the magnetic field region by the rotation of the drum and are duly discharged while leaving the magnetic field region. Such drum-type magnetic separators are disclosed, for example, in Bulletin no. H26 of Dings magnetic Group, pp. 1-3, and Handbook 390 “Laboratory and Pilot Size Materials Testing and Handling Equipment for the Process Industries”, pp. 67-68.
International Application WO 2000/25929 describes a method and apparatus for magnetic separation of a first component having relatively strongly magnetic properties from a mixture containing the first component and at least a second component having relatively weakly magnetic properties, as compared to those of the first component. A magnetic field source is mounted on a circumference of a drum and rotated in a certain direction with a predetermined speed. The magnetic field source creates a magnetic field region in the vicinity of the drum. The mixture is fed into a separation channel, which is stationary mounted in the vicinity of the drum, and extends along a circumferential portion of the drum. The rotation of the drum can cause the movement of the first component along the separation channel in a direction opposite to the direction of the rotation of the drum. The first and second components are discharged through opposite ends of the separation channel.
A common problem of conventional techniques mentioned above is associated with the undesirable effect of “flocculation”, described as follows. When magnetizable material passes through a magnetic field region, it becomes magnetized. Each particle of such material presents a separate magnet having opposite pole pieces. Magnetic forces occurring between these particles cause their conglomeration, trapping non-magnetic material therebetween. This reduces the quality of the separation. In such cases, at least one additional stage of magnetic separation is required.
In some applications, therefore, separation of the materials is performed manually by visual recognition of pieces of different pieces and objects. It is needless to say that the cost of manual separation is considerable, especially in the case of small pieces, for example, used in production of micro-electronic components, such as miniature resistors, capacitance, active elements, etc. As for the manual separation of small ferromagnetic balls (media) used in the Nickel coating process, from Nickel coated electronic components (chips), the use of a microscope is usually required.